The man who aims to oust the Italian prime minister, Silvio Berlusconi, yesterday accused his rival of trying to cheat and buy his way back into power at the next general election, which is less than six months away.

Opening his campaign with an unprecedentedly hard-hitting interview, Romano Prodi, the former president of the European commission, told the Guardian that Italy would be finished if the media tycoon were returned to office.

"If there is no change, Italy is finished, because this government is utterly incapable of taking bold decisions. The only laws that have made it through parliament, notwithstanding [the right's] huge majority, have been those that have conferred an advantage either on the prime minister or his friends."

Mr Prodi said that although opinion polls put him clearly ahead, he had no illusions about the difficulties he faced. Angela Merkel's experience in last month's German election had shown how a strong lead in polls could be whittled away.

But in Italy's case, said Mr Prodi, there was a concerted attempt by the prime minister to alter the odds in his favour. "Berlusconi has already begun, putting in an amount of money that has no precedent - and here I am not exaggerating - a sum of money that has no precedent, not just in the history of Italy, but in the history of Europe," he declared.

Mr Prodi said the prime minister's aides had spoken explicitly of €1m (£675,000) for every marginal constituency. He claimed that altogether his billionaire rival was preparing to add a minimum of €250m to the money his party received from the state for its campaign. In addition, the opposition fears the prime minister is poised to fund a barrage of TV commercials. Mr Berlusconi has announced that he intends to revoke a law that bans political advertising in the final stages of a campaign.

The prime minister insists he himself is the victim of media bias. In an interview for a forthcoming book, leaked at the weekend, Mr Berlusconi named seven comedians whom he accused of using the state-owned network, RAI, to launch satirical attacks on him. The last time the prime minister publicly identified a series of television personalities who had annoyed him - three years ago - they disappeared from the country's screens.

Mr Berlusconi was commenting on a programme last week that featured one of those personalities, appearing on television for the first time since the 2002 criticisms. The prime minister, who owns Italy's three biggest commercial channels, said the programme was "the latest episode of a system of communication, television and also press, which from 2001 has systematically attacked the work of the government and the prime minister".

In an interview with the Guardian and four other European newspapers, Mr Prodi said his opponent's grip on television was already a big handicap. Figures gathered the last time he stood against Mr Berlusconi, in 1996, showed that the number of electors in each category who voted for him was inversely proportionate to the number of hours spent in front of the television. However, if the existing rules governing campaign broadcasts were to be abolished, he would have to compete with Mr Berlusconi for advertising time on the prime minister's own channels. "I would have to fund the prime minister, which seems to me a pretty bizarre thing even for a bizarre country," he said.

The former economics professor is the only man to have beaten Mr Berlusconi at the polls. He returned from Brussels last year and earlier this month he won a notable victory at primary elections held to select the left's candidate. The organisers claimed a turnout of 4.3 million - more than double the most optimistic forecast - and said almost three-quarters opted for Mr Prodi.

Battle for power

· Silvio Berlusconi wants Italy's first general election since 2001 to be held on April 9 next year. The date must be rubber-stamped by the president.

· The right will be represented by Mr Berlusconi's House of Freedoms coalition. This includes his Forza Italia party, the formerly neo-fascist National Alliance, a conservative Christian Democrat party and the regionalist-populist Northern League.

· Mr Prodi's nine-party alliance of the centre and left takes in the former communists and the more progressive wing of the old Christian Democrat party. It also includes Greens, socialists and anti-graft campaigners.

· A bill would replace the system in which three-quarters of MPs are chosen on a first-past-the-post basis with full proportional representation.